alex-shamshurin

'use strict';
class Abstract {
  // A static abstract method.
  static foo() {
    if (this === Abstract) {
      // Error Type 2. Abstract methods can not be called directly.
      throw new TypeError("Can not call static abstract method foo.");
    } else if (this.foo === Abstract.foo) {
      // Error Type 3. The child has not implemented this method.
      throw new TypeError("Please implement static abstract method foo.");